A neural circuit at the base of mouse brains drives a loneliness-like state and motivates the animals to seek company.

Kay Tye at the Massachusetts Institute of Technology in Cambridge, Mark Ungless at the Medical Research Council's Clinical Sciences Centre in London and their colleagues found that connections between neurons in the circuit were stronger in mice that were separated from their cage mates than in those that were grouped together. Those neurons then fired more frequently when isolated mice were put in a cage with an unfamiliar mouse, compared with animals that had not been isolated. When the scientists inhibited the neurons with light, the isolated mice showed less interest in the stranger. Activating those neurons caused the animals to actively seek other mice.

The circuit was more responsive in socially dominant animals.

Cell 164, 617–631 (2016)